A laser welding method for resin material is well-known. A laser beam is irradiated on light-absorption resin material through translucent resin material so that a connection portion between the light-absorption resin material and the translucent resin material is welded.
To improve connection property, for example, to reduce generation of a burr and a void, a protrusion is formed on a bonding surface of the translucent resin material. A part of the translucent resin material that is disposed outside of a laser beam irradiation area presses the light-absorption resin material. Then, the laser beam is irradiated on the protrusion. Thus, the resin material is welded by the laser beam. This laser beam welding method is disclosed in JP-A-2004-358697 corresponding to US Patent Application Publication No. 2004/0239007. Further, JP-A-2005-288934 corresponding to US Patent Application Publication No. 2005/0218123 discloses that the vertical cross section of the protrusion is a triangle shape. This method is described in FIG. 2. In FIG. 2, a reference numeral 101 represents the light-absorption resin material, 102 represents the translucent resin material, and 103 represents a triangle protrusion.
A periphery portion of a translucent resin cover is welded on an upper sidewall of an opening portion of a light-absorption resin vessel, as shown in FIG. 3.
In FIG. 3, a reference numeral 20 represents a sidewall of the light-absorption resin vessel, 21 represents the upper surface of the sidewall 20, and 22 represents the translucent resin cover. A reference numeral 23 represents a triangle protrusion disposed on the upper surface 21, 24 represents a rib, which stand from the upper surface 21 along with the outer periphery surface 25 of the sidewall 20. A pressing jig 26 presses a part of the translucent resin cover 22, which is disposed outside of the laser beam irradiation area. When the laser beam 27 is irradiated on the translucent resin cover 22, the protrusion 23 melts, so that the translucent resin cover 22 is pressed by the pressing jig 26. Thus, the translucent resin cover 22 moves, i.e., turns down toward the upper surface 21 of the sidewall 20. Because of this displacement of the translucent resin cover 22, the melted resin of the protrusion 23 moves to both sides of the protrusion 23 so that the melted resin fills a small concavity and convexity of the upper surface 21 of the sidewall 20. At this time, generated gas and residual air disposed near the upper surface 21 are pushed aside by the melted resin moving away from the protrusion 23, so that the gas and the air are discharged to both sides of the protrusion 23. As a result, the bottom of the translucent resin cover 22 is sufficiently welded on the upper surface 21 of the sidewall 20. Here, in FIG. 3, the upper surface 21 of the sidewall 20 from a bottom side adjacent to the protrusion 23 to the rib 24 slopes toward the rib 24. Alternatively, the upper surface 21 may be flat.
However, in the above conventional laser beam welding method with the triangle protrusion, a micro clack may be generated in the translucent resin cover 22.